Simultaneous biaxial drawing process for polyamide films

ABSTRACT

PROCESS FOR IMPROVING THE UNIFORMITY OF BIAXIALLY DRAWN POLYAMIDE FILM BY MAZIMIZING THE TRANSVERSE TO LONGITUDINAL DRAW MAGNIFICATIONS DURING THE FIRST 40% OF SIMULTANEOUS BIAXIAL STRETCHING.

Jan. 4, 1972 MUTSUO KUGA ET AL 3,632,128

SIMULTANEOUS BIAXIAL DRAWING PROCESS FOR POLYAMIDE FILMS Filed Dec. 31, 1968 2 Sheets-Sheet 1 fig: .1

(Q "3 I g 15- Q) E 0 WIDTH 105m) 1-] 2 1 7 J 15 33 51a- 2 E 0 WIDTH /0b(% Jan. 4, 1972 v MUTSUO KUGA EI'AL 3,632,728

SIMULTANEOUS BIAXIAL DRAWING PROCESS FOR POLYAMIDE FILMS Filed Dec. 31, 1968 2 Sheets-Sheet 2 THICKNESS WIDTH mom) United States Patent Ofice 3,632,728 Patented Jan. 4, 1972 3,632,728 SIMULTANEOUS BIAXIAL DRAWING PROCESS FOR POLYAMIDE FILMS Mutsuo Kuga, Kyoto-shit, and Takeshi Mashimo, Teruo Arai, and Yoshihiko Yano, Kyoto-fu, Japan, assignors t Nippon Rayon Kabushiki Kaisha (Nippon Rayon Co., Ltd.), Kyoto-fu, Japan Filed Dec. 31, 1968, Ser. No. 788,263 Int. Cl. B29d 7/24 U.S. Cl. 264289 3 Claims ABSTRACT OF THE DISCLOSURE Process for improving the uniformity of biaxially drawn polyamide film by maximizing the transverse to longitudinal draw magnifications during the first 40% of simultaneous biaxial stretching.

BACKGROUND OF THE INVENTION We have described and claimed in U.S. Patent No. 3,502,766, based on patent application No. 734,212, filed June 4, 1968 (which is incorporated by reference) processes for producing polyamide films involving the simultaneous and biaxial drawing of a substantially amorphous polyamide film. In such processes, drawing is effected in both longitudinal and transverse directions at a draw speed of from 6,000 to 100,000%/min. and at a temperature within the range of from 70 to 180 C. which is at least 35 C. below the melting point of the film. The ratio of the longitudinal to transverse draw speeds is generally from 2:1 to 0.5 :1 and the draw ratio is from 16:1 to 4:1. The polyamide films obtained by these processes have various advantages such as improved tensile strength and optical clarity for general uses in addition to very even surface, high transparency and beautiful luster.

But there is still admitted a margin for improvements because of insufficient yield on starting material. This is true since the deviation from the mean value in thickness of the simultaneously and biaxially drawn polyamide film is liable to be larger than that found in the so-called listing area or selvage which is located in the neighborhood of the tenter clips of guide means used in catching and guiding the film in drawing. This phenomena may be caused by the fact that the draw magnification in the transverse direction is liable to increase on both sides thereof, particularly at the listing area rather than in the center area. It would be advantageous for improving the yield on starting material if means could be found to equalize the difference between the draw magnifications in the central and listing area.

SUMMARY OF INVENTION According to the present invention, we provide an improved process for drawing polyamide films, in which a substantially amorphous polyamide film is drawn simultaneously and biaxially in the longitudinal and transverse directions at a draw speed of from 6,000 to 100,000%/min. and at a temperature within the range of from 70 C. to 180 C. which is at least 35 C. below the melting point of the film, the ratio of the longitudinal and transverse draw speeds being from 2:1 to 05:1 and the draw ratio being from 16:1 to 4:1, (as defined in Ser. No. 734,212 which is incorporated by reference) whereby the film is drawn so as to pass, when the ratio between the average thickness of the drawn film and that of the initial film is still at least 0.6:1, through an area where the magnifications in both directions would be at the maximum, said maximum being more than 1.3.

By the process of this invention, it is now possible to obtain simultaneously and biaxially drawn polyamide films which have aforesaid advantages without any deteriorative effect on starting material. The films obtained have an even and uniform thickness throughout the whole area including the neighborhood of the tenter clips or guide means.

Behavior of synthetic linear polyamide films varies with their water content. As described in our pending U.S. patent application No. 578,449, even thickness and homogeneous physical properties of simultaneously and biaxially drawn polyamide films can largely be improved in the longitudinal direction by addition of a small amount of water.

According to another feature of the present invention, it is also preferred to use raw polyamide film having a water content of more than about 1% by weight of polyamide, when polyamide having a water-absorbability are used for the purpose of the present invention, which is also useful for improving the physical properties in the transverse direction.

Various conditions such as for example pre-heating temperature, water content of the film, etc. depend upon the type and thickness of the film to be drawn, etc. An excessively high temperature is liable to deteriorate the film properties, and poor temperature such as below 60 C. is also disadvantageous. A water content of more than 1% by weight of the film is generally sufficient for obtaining a better heat transmission in pre-heating and the film is heated uniformly so as to give a uniform and even thickness to the drawn film throughout the whole area with a good yield.

In this application, the proportion of draw magnification in the transverse and longitudinal directions is hereinafter designated as P. Thus P=draw magnification in the transverse direction per draw magnification in the longitudinal direction, in which draw magnifications are measured at an optional point of the drawn film.

Draw magnification is h /h and l /l wherein h, and are, respectively, the width and length of undrawn film measured between 2 optional points thereon. I1 and I are, respectively, values after drawing.

According to our discovery, at the early stage of drawing just when the thickness of the partly drawn film is still at least 60% of that of the undrawn film, the drawn film should be passed through a certain area where the proportions of draw magnifications ratio P would reach to its maximum value, said maximum value being more than 1.3.

In drawing simultaneously and biaxially polyamide film, the film is pre-heated and is then drawn simultaneously and biaxially by passing through a predetermined film track or locus. During drawing, the P value varies within a predetermined range due to the fact that the film is drawn on a divergent locus. The present invention teaches that the drawn film should be passed through a certain area, where the P value is at maximum, at the early stage of drawing. This can only be achieved by using the locus according to the present invention in which the film is drawn simultaneously and biaxially at a larger drawn magnification in the transverse direction than that in the longitudinal direction at the early stage of drawing.

In this specification, the term polyamide films include in general films made of any and all substantially amorphous synthetic liner polyamides for example as follows: poly-ecaproamide, poly hexamethylene adipamide, poly-hexamethylene sebacamide, poly 11 amino undecanamide, poly-laurineamide, copolymerized polyamide and mixture of two or more thereof etc.

Drawings:

FIGS. 1, 2, 3, 4 and 5 show respectively the deviation from the mean value in thickness of the drawn films obtained from Examples 1 t 5.

[Experimental data:

In the following tables and examples, the width of the film deviates the distance from inside a tenter clip (guide means) catching the film to the inside of the corresponding tenter clip located at the opposite side of the film taken perpendicular to the longitudinal direction (i.e. across its width.)

Key to tables Athickness of the film in the area where the P value is maximum (thickness of the undrawn raw film=1) BP value (maximum) Crange of the P value D-width having a uniform and even thickness (mm) E-width having a uniform and even thickness per total width of the drawn film TABLE 1 1 D, percent Sample Polyamide No. A B C 4 6 Polye-caproamide 1 0. 7 1. 8 1. 0-1. 8 1, 320 1, 440 2 0.3 1. 8 1. 0-1. 8 1, 125 1, 305

Polylaurlne amide 5 0.7 1. 8 1. 0-1. 8 1, 300 1, 440 e 0. 3 1. s 1. 0-1. s 1, 130 1, 295

1 Total width of film measured at outlet of drawing zone was 1,500 mm.

TABLE 2 A B C D/i 4% TABLE 3 E, percent TABLE 4 E, percent;

A B C =l=4 =l=6 Table 1 In Table 1, it is shown that the width having a uniform thickness (D) was liable to vary considerably according to the change of the position offering a maximum P value, when raw polyamide films having a thickness of about 15 81-4 11 were drawn at a final draw magnification of 3 in the longitudinal direction and 3.5 in the transverse direction with a draw speed of about 36,000%/min. and at a P value of from 1.0 to 1.8 or 1.0 to 1.5. The raw film were 4 made of poly-e-capro-amide and poly-laurinamide, which are similar to those used in Examples 1 and 2.

The draw temperature of the former was 170 C. and that of the latter was 130 C. The total width of the drawn film was 1500 mm.

Table 2 In Table 2 a raw polyamide film (666 mm. in width) made of poly-e-caproamide having a water content of 4.5% by weight at the beginning of drawing [initial thickness 200 was processed. The film had a final draw magnification of 3.0 both in the transverse and longitudinal directions and at a P value within the range of from 1.0 to 1.7. The film was pre-heated to C. The density of the film was 1.130.

From Table 2, it is shown that the proportion between the width having a uniform thickness and the width of the total drawn polyamide film varies largely according to the change of the position, at which the P value reaches to its maximum.

From Tables 1 and 2, it is apparent that more than about of the total width of the drawn film can be provided with a uniform and even thickness almost throughout the whole area, even though the drawn film has a relatively narrow width of 666 mm., by drawing the film simultaneously and biaxially so as to pass through a certain point, at which the P values reaches its maxiumum, said maximum being more than 1.3, at an early stage of drawing where the ratio between the average thickness of the drawn film and that of the raw film is more than 0.621. Otherwise, the obtained films are more or less deteriorative.

Tables 3 and 4 The results shown in Table 3 are obtained by drawing simultaneously and biaxially a raw poly-caproamide film having an initial thickness of 4 by using different tracks to give different drawn film under the following conditions:

Table 3a Water content at the beginning of drawing (per- In Table 4, a raw poly-e-caproamide film is simultaneously and biaxially drawn by using different tracks to give different drawn films under the following conditions:

Table 4a Final draw magnification in the transverse direction 2.5 Final draw magnification in the longitudinal direction 3.0 Water content at the beginning of drawing (percent by weight) 4.0 Density of the film 1.130 Width of the film mm 800 Pre-heated temperature t C 80 P value 0.8-1.4

From Tables 3 and 4, it is apparent that drawn polyamide film having uniform and even thickness can be advantageously obtained according to the process of the present invention, even when drawn at different final draw magnification ratios in the transverse and longitudinal directions.

In this specification, the wording a drawn film having a uniform and even thickness means a drawn film of which minimum or maximum thickness deviates from the average thickness in an amount of within i6%. Among films having uniform and even thickness those having the deviation of within 4% are highly evaluated. In the following non-limitative examples illustrating the invention, the wording uniform and even thickness means the deviation of the thickness of within i4% from the mean value.

X-ray was used to determine the thickness of the drawn film in the transverse direction.

EXAMPLE 1 -A substantially amorphous film (density of 1.130 g./cc., thickness 0.135 mm.) of poly-e-caproamide was pre-heated to 170 C. by using infra-red heaters.

Immediately after this, the pre-heated film was drawn simultaneously and biaxially with a draw speed of about 24.000%/min. at 170 C. to give a film with a final draw magnification of 3 in both the longitudinal direction and transverse direction at a P value of from 0.9 to 1.5. At a maximum P value of 1.5, the ratio between the thickness of partly drawn film measured in this area and that of the undrawn film was 0.8.

Then the drawn film was heat-set at 215 C. in hot air to give a film having a width of 1800 mm.

FIG. 1 depicts the results obtained from the film.

The film obtained in this manner had a uniform thickness of :0.6 t in the range of 96% of the total width.

EXAMPLE 2 A substantially amorphous film (density of 1.009 g./cc., thickness 0.16 mm.) of polylaurineamide was pre-heated to 120 C., by using infra-red heaters. Immediately after this, the pre-heated film was drawn simultaneously and biaxially with a draw speed of about 32,000%/min. at 120 C. to draw a film with a final draw magnification of 3 in the longitudinal direction and 3.5 in the transverse direction, at a P value of from 1.0 to 1.7. At a maximum P value of 1.7, the ratio between the thickness of partly drawn film measured in this area and that of undrawn filrn was 0.7. Then the drawn film was heat-set at 160 C. in hot air to give a film having a width of 1680 mm.

The results obtained from the film are shown in FIG. 2.

The film obtained in this manner has a uniform thickness of 15 +0.61]. in the range of 97% of the total width.

EXAMPLE 3 A poly-e-caproamide raw film having a relative viscosity of 2.7 when measured at 25 C. by using 96% H 80 and a density of 1.128 was processed by using the T-clie process to give a substantially amorphous undrawn polyamide film having a thickness of 25 which was adjusted to contain 4.5% (by weight) of water. The undrawn film was pre-heated to 80 C. with infra-red heaters. Immediately after this, the film was drawn simultaneously and biaxially with a drawn speed of about 32,000%/mm., to give a final draw magnification of 3 in both the transverse and longitudinal directions, and was then heat-set at 200 C. in hot air. In this manner, two types of the drawn films were obtained with the differences as follows:

The results obtained from both films are shown in FIG. 3, from which it is apparent that the film A had a proportion of its width having a uniform and even thickness to the total width of the drawn film of almost 100%, while film B had a corresponding proportion of less than 85%.

EXAMPLE 4 A substantially amorphous undrawn film (thickness 135p.) was made of poly-1l-amino-undecanamide (relative viscosity when measured by 25 C. by using 96% H SO -2.7 density1.030) by the T-die process. The film was adjusted to have a water content of about 1.7 0/ 0% and pro-heated to C. by using infra-red heaters. Immediately after this, the pre-heated film was drawn simultaneously and biaxially to give a final draw magnification of 3 both in the transverse and longitudinal directions. The drawn film was heat-set at 200 C. in hot air and was cooled. 'In this manner, two types of the drawn films were obtained with the following differences:

Type of drawn film Minimum P value 0.7 0. 7 Maximum P value 1. 3 1, 1

Ratio between the thickness of the drawn film at the point where the P value reaches to its maximum, and that of the undrawn film. 0 7

. 0.25 Width of the drawn film (mm.) 1,000

EXAMPLE 5 A substantially amorphous undrawn film was prepared by using the T-die process. Poly-e-caproamide as raw material had a relative viscosity of 2.9 at 25 C. measured by the use of 96% H 80 and a density of 1.128. The undrawn film obtained having a thickness of was adjusted to a water content of 5% by weight and was preheated to 80 C. using infra-red heaters. Immediately after this, the preheated film was drawn simultaneously and biaxially to give a final draw magnification of 3 both in the transverse direction and 3.5 in the longitudinal direction. The drawn film was heat-set at 200 C. in hot air and was cooled. In this manner, two types of the drawn films were obtained with the following differences:

,B-Ray was used to determine the thickness of the drawn film in the transverse direction. The results obtained are shown in FIG. 5, from which it is apparent that the film A is superior to the film B regarding the proportion of its width having uniform and even thickness to the total width.

Having described the present invention, what is sought to be protected is set forth in the following claims.

1. In a process for drawing improved polyamide films wherein a substantially amorphous synthetic linear polyamide film is drawn simultaneously and biaxially in the longitudinal and transverse directions at a draw speed of from 6,000 to 100,000%/min. and at a temperature within the range of from 70 C. to 180 C. which is at least 35 C. below the melting point of the film, the ratio of the longitudinal and transverse draw speeds being from 2:1 to 05:1 and the draw ratio being from 16:1 to 4:1, the improvement which comprises drawing the film so as to pass at an early stage of drawing when the ratio between the average thickness of the drawn film and that of the initial film is still at least 0.6:1, through an area where the proportion of draw magnification in the transverse and longitudinal directions would be at the maxi- 3,193,873 7/1965 Wienand 264289 mum, said maximum being more than 1.3. 3,248,753 5/1966 Kobayashi et a1 264289 2. The process of claim 1 wherein said film to be 3,256,379 6/1966 Hefielfinger 264289 treated has a water content of more than 1 weight percent. 3,502,766 3/ 1970 Tsuruta et a1. 264210 3. The process of claim 1 wherein after drawing the 5 3,510,552 5/1970 Tsuruta et a1. 264289 film at least 90% of the film deviates by no more than from the mean thickness I. Primary Examiner References Cited H. MINTZ, Assistant Examiner UNITED STATES PATENTS 10 US. Cl. X.R.

2,352,725 7/1944 Markwood 264288 26078S 3,046,599 7/ 1962 Nicholas et a1. 264289 

